392 upgrade suggestions (Mac1 parts?)

[Hack21]

I have a 2014 392 that is basically stock. I added the requisite peep sight, removed the factory rear sight, removed paint from inside of the muzzle and from the front post, stoned the hammer edges, and performed the typical polishing/lubing/spring lightening that apples to the trigger. It shoots well and handles great.

I talked to Tim about doing a steroid tune on it. The durability enhancements and efficiency gains appeal to me. However, I don't need that much power and don't care to spend that much money either. Also, the stock gun is quite loud at 8 pumps already for my back yard and I enjoy tinkering myself.

So this is what I am thinking and would love some input. 

Tim sells a kit of steroid parts to update the pump to more durable components. The adjustable piston should dramatically improve efficiency. These parts are legendary and should outlast me. I would install these myself.
 http://www.mac1airgunshop.com/sheridan-rocker-bolt-lug-p/m1bilevki.htm

So then to the valve... I don't know what all Tim does, but I do know that his exhaust valve requires the seat geometry to be altered.  I was thinking about using a discovery exhaust valve 1761A140 with the original seat instead. It would take more force to open than Tim's and likely wouldn't dump as many pumps, but it would be readily available and wouldn't require machining. I was told that the synthetic stock version of the gun that they sell now uses this part and I suspect that it has a lot to do with them now being rated for 10 pumps. I also would do the two spring mod and some porting. I would grind the valve stem diameter down in the throat area.  Adding an additional o-ring grove on the transfer port would help. I would replace all of the orings with cast polyurethane.

Lastly would be to do the two stage adjustable trigger modifications that I applied to my AS392 HPA conversion. https://www.gatewaytoairguns.org/GTA/index.php?topic=166326.msg155860888

So the idea would be to make it more efficient and as bulletproof as possible with a vastly improved trigger. The power would be more than stock but not Steroid levels. I would be a third of the way to steroid cost with the satisfaction of doing the work myself.

Has anyone installed Tim's pump kit and have feedback? Will I regret not leaving it stock or sending it to Tim to get the entire thing done? Thoughts?

Thanks.

[Van]

         I installed the Mac 1 pump arm kit myself without the steroid valve.  The big improvement was in the solid pumping feel and the adjustable pump rod.  The stock FPS was only 640 at 8 pumps with 14.3g pellets.  After adjusting the rod for as close to 0 head space as I could get, it went to 665fps on 8 pumps and 720fps on 10 pumps.  I was very happy with just the kit.  The only other things I did inside the gun were to change to an AS392 exhaust valve, which has a harder seal material, the two spring mod, which makes the first couple of pumps easier, and a super sear which improved the trigger.  I also thinned the stock and pump arm wood for a less chunky look.   

[Hack21]

         I installed the Mac 1 pump arm kit myself without the steroid valve.  The big improvement was in the solid pumping feel and the adjustable pump rod.  The stock FPS was only 640 at 8 pumps with 14.3g pellets.  After adjusting the rod for as close to 0 head space as I could get, it went to 665fps on 8 pumps and 720fps on 10 pumps.  I was very happy with just the kit.  The only other things I did inside the gun were to change to an AS392 exhaust valve, which has a harder seal material, the two spring mod, which makes the first couple of pumps easier, and a super sear which improved the trigger.  I also thinned the stock and pump arm wood for a less chunky look.   

That looks great. How did you extract the roll pins that secure the pump handle to the linkage? The wood is drilled blind (not the entire way through). My thoughts were to try to get a bite on the inside of the roll pins with a drywall screw or similar and then using a slide hammer to tug them out. Otherwise, a drill bit passed through the ID of the roll pin and then enlarging the newly created pilot hole from the other side of the handle so that the pins could be driven through.

[Van]

    The method of drilling through the hole in the roll pin then enlarging the resulting small hole on the blind side worked great.  Then I punched out the pins with a correct size punch that was the same size as the roll pin outside diameter.  They make a special type or roll pin punch but a regular one works fine if it's the right size.  Here is a better picture of the stock.  I used solid rod instead of the roll pins as I hate those things.   The small LDC is made from PVC parts, washers and brass tube,then epoxied on.   

[Hack21]

    The method of drilling through the hole in the roll pin then enlarging the resulting small hole on the blind side worked great.  Then I punched out the pins with a correct size punch that was the same size as the roll pin outside diameter.  They make a special type or roll pin punch but a regular one works fine if it's the right size.  Here is a better picture of the stock.  I used solid rod instead of the roll pins as I hate those things.   

Perfect - great info and exactly what I was looking for. Did you add the white detail on the butt stock pad also? 

I knew that the AS392 exhaust valve part number was different, but I didn't know the what or why. It having a harder material makes sense. My AS392 chewed through one in 2000 pellets or so at 1100 psi with a significantly larger valve volume. I do have 2 AS392 exhaust valves that I could use. It seems like the disco exhaust valve would be more durable, but harder to seal. The additional spring preload from the 2 spring mod should help though. Thoughts?

[Van]

  I did add the white spacer to the stock, made from a scrap piece of white plastic cut and sanded down with the original butt plate installed, to match the thinner wood stock.  I did not try a Disco valve seal, but the AS392 sealed after installing and spinning with a hand drill attached to the stem for a moment to set it to the seat. It has the hard material which lasts longer and performs better than the soft stock seal.   

[Hack21]

Van,

How effective is that LDC? I had thought that it might work well to drill and tap the plug that installs below the barrel. It could then be used to bolt a printed LDC on that mated to the plug and slipped over the barrel. It would be an odd part, but might work well and would be easily removable.

My 392 makes exactly 640fps on 8 pumps with 14.3s also. I had to install a new pump cup and the 1/8" pin that Tim rightfully rants about is bent and increasing the pump cup clearance. The stock pump parts are pretty flimsy on the late model guns.

Thanks.

[Van]

  The thing I made on that 392 gun was pretty effective at changing the report from a sharp crack to a much lower sound.  I did not do a sound meter check but was happy with it on that gun.  There are some older post on the net where people did bolt an LDC to the plug but were not too happy with it.  There are slip on adapters that mount with a set screw on Ebay.  They work well but are threaded 1/2 -20.  I used one on this Dan and made a cut down LDC from a Benjamin Trail LDC core.  The Trail cores can make a very effective LDC and are threaded 1/2-20.   I just like the lower sound although its not necessary here as not in city and no close neighbors.  I do like them to be easy to remove and should not be too long.  That Mac1 pump kit cures all problems with the weak stock pump on a 392.   

[Hack21]

I ordered the Mac1 billet pump kit today. I will capture some before and after chrono numbers to share results when I eventually complete it. I called Crosman and they indicated that the exhaust valve was unchanged for the 392S and that the stock was the only changed item.  I don't have one to tear down to confirm if this is true or if they are indeed now using the disco exhaust valve. So I am on the fence about using the disco exhaust valve or the AS392 exhaust valve.  I am leaning towards the disco stem and if it doesn't hold 2 pumps indefinitely, then swap it for the AS392 stem.

When doing the two spring mod, do most people reuse the spring or replace it for a shorter and/or softer spring?  Is there a trigger spring part number or similar that works well for the second spring?

Thanks.

[Van]

  For the 2 spring valve mod I just bought an assortment of stainless steel springs in the correct OD and various strengths from Ace Hardware.  It took some trial and error cut to length to find a good combo.  All it really improved was the first few pumps were easier.  The softer spring installed on the valve intake side does allow it to open easier on the first few pumps, then the pressure builds so the next ones start to feel like the stock spring.  It was fun to experiment but not a lot of difference if you usually do 6 or more pumps.  Stainless springs do not rust like regular steel ones do in the valve.

[Hack21]

The pump kit arrived today well packaged after being shipped very promptly. I had the pleasure of speaking to Tim on the phone several weeks ago and my impression was that he doesn't compromise on quality. The parts are impressive so far (not yet installed). The parts fit tightly with nice radiuses where they should be. The rivet was already set pinning the link to the pump arm.  Thank you Tim!

[Hack21]

I know this is a pretty straightforward project, but I will provide an update as I enjoy reading of other's projects and it may be a helpful resource to someone someday.

My plan was to gather a good set of baseline chrony numbers. I was planning to then install the adjustable piston and get a second set of numbers prior to doing some valve work as the final step. However, I had a leak that prevented this. I believe it was either the pump cup or the o-ring on the outside of the valve.  Either way, it is fully disassembled now and the only numbers will be the final numbers. 

I did as Van stated and drilled through the inside of the roll pins with a number drill.  I used a loose 1/4" chuck and turned it by hand. I then drilled this hole larger from the other side in small steps until I got to 1/8" (also by hand).

I have seen some of these values elsewhere, but not all of them.  I measured flow path diameters as follows:.

Valve throat 0.221"
Exhaust valve stem 5/32 (0.156")
Valve port 0.164ish"
Barrel port 5/32 (0.156") (complete with sharp edges)
Bolt probe 1/8 (0.125")
Leade 0.22ish"

As Bob has stated before, it looks like the throat is the smallest passage. I will grind the stem down to 1/8 (0.125") in this area.  The barrel port is the second smallest passage and I will blend the corners and possibly open it up to 0.161".  I will also need to do some deburring and work on the leade in general.

The valve seat appears to have a small nick that will need to be lapped out.

I was surprised how much crude was loaded up in the system. I suspect some of it was paint overspray from inside the pump tube that was worn free. I will try to remove the remainder of the overspray with solvent while it is apart.

Thanks.

[Van]

  Eric,  You may already know this but I will mention it here.  When you set up the adjustable pump rod and cup seal take off the outside O rings on the valve before temporarily installing it.  This lets you set the rod for zero headspace without the pressure working against you.  You will like that kit. It's the bet thing you can do to a 392 in my opinion without sending it in to Mac1.

[Hack21]

  Eric,  You may already know this but I will mention it here.  When you set up the adjustable pump rod and cup seal take off the outside O rings on the valve before temporarily installing it.  This lets you set the rod for zero headspace without the pressure working against you.  You will like that kit. It's the bet thing you can do to a 392 in my opinion without sending it in to Mac1.

Van,

Thanks for the suggestion. I was thinking about making a "degas" tool to hold the exhaust valve open as it could also be handy for my AS392 HPA conversion also. Your suggestion is a lot simpler. I assume you could slip a drill bit in place of the roll pin for this activity as well?

Thanks.

[Van]

   A drill bit body works if it's the right size with no slop.  I replace the roll pins in my pumpers with a snug fitting solid rod with C clips on the ends.  I   make them on the drill press ,after cutting to length, by spinning against a mini hack saw blade to cut the groove.   Roll pins tend to mess up tubes driving them in and out to change seals or springs.  Solid pins remove and install much easier.  Just keep them lubed with the secret sauce. 

[RBQChicken]

I buy 3/16" by 1" long dowel pins at my local hardware store. They're only about 1/16" longer than the stock roll pins, and I find I don't need any clips for them to stay in place.  You're right, much easier to drive in and remove, if necessary.

[Hack21]

Thanks for the recommendations Van and Randy.  Both seem like good solutions. 

[Hack21]

I have been geeking out on the math trying to find the ideal springs to execute the two spring valve mod. I did find some readily available spring options that may work reasonably well, but that quest led me to the following question. Are the factory valve springs plated or simply coated with oil? Mine had a little bit of corrosion on it, so if it is indeed plated, then I am wondering how well a an unplated music wire spring will hold up in that environment? 

Thanks.

[Hack21]

Does the adhesive backed felt get adhered to the wood pump handle or the tube? I would think either would work with it probably having a nicer appearance attached to the wood grip but probably adhering to the tube more dependably?

Also, I will bump my question again. Are the valve springs plated or simply oiled? 

I assembled the pump mechanism to see if the piston length would need to be increased or decreased and imagined that it would take several iterations to get it dialed in perfectly. Amazingly it came from Mac1 perfectly adjusted. I don't know if it was dumb luck or if he has a fixture that he uses to adjust them, but it was a nice surprise!

[Psipumper]

Does the adhesive backed felt get adhered to the wood pump handle or the tube? I would think either would work with it probably having a nicer appearance attached to the wood grip but probably adhering to the tube more dependably?

Also, I will bump my question again. Are the valve springs plated or simply oiled? 

I assembled the pump mechanism to see if the piston length would need to be increased or decreased and imagined that it would take several iterations to get it dialed in perfectly. Amazingly it came from Mac1 perfectly adjusted. I don't know if it was dumb luck or if he has a fixture that he uses to adjust them, but it was a nice surprise!

I need to try the felt trick. I think stick it to the handle.
Haven’t paid much attention to the spring plating. I usually use the same spring as the hammer cut to length. That one has some sort of bright plating . I have even compressed the spring on a rod and waved the torch over it to reduce the spring rate before cutting to length.
When the adjustment is correct on the piston length, the pump arm should be like this photo.